Canadian Patent. No. 1,158,466 issued Dec. 13, 1983 to Litton Systems, Inc. discloses an optical slip ring which uses a pair of axially spaced apart graded index rod lens to effect efficient optical coupling between a pair of relatively rotating optic fibers. In the structure of the patent one lens is mounted in a stator and is connected to one optic fiber while the other lens is mounted in a rotor and is connected to the other optic fiber. A small gap separates the rotor and stator lenses. The lenses used are SELFOC (trademark) lenses, available from NSG America, Inc. of Clark, N.J., U.S.A.
Optical fibers are relatively fragile and care must be taken with a single channel rotary joint to avoid breakage of the fibers used. It is desirable to be able to reduce the concerns respecting breakage especially where either the environment is inhospitable to the equipment or the joint is relatively inaccessible when in use, as for example when it might be used in undersea applications.